Nuclear magnetic resonance (NMR) imaging is a powerful diagnostic tool with widespread potential applications. Currently, the literature on the bioeffects of NMR is incomplete, inconclusive, and mostly confined to mature animals. Too few studies have been done to evaluate the risks of NMR exposure during development. Since the developing fetus is most susceptible to teratogenic agents, and may react to static and dynamic mapetic helds, and to tissue heating produced by radiofrequency radiation during NMR exposure. a systematic study to investigate the relative safety of NMR exposure during development is required. Tbe proposed research will determine: 1) any critical periods of sensitivity; 2) the statistical occurrence of any structural abnormality; 3) any functional and behavioral abnormalities subsequent to NMR exposure during development. In addition, the effects of NMR on the developing nervous system, an organ system that is most suseeptible to any teratogeztic agenu, will be investigated. More specifically, NMR effects on three critical processes that give rite to the highly precise nervous system will be evaluated: 1) the migration of neural crest cells; 2) the projection pattem and timing of axonal growth; 3) specific synapse formation. Crucial to any scientific study is the experimental model system. In this study, the chick embryo was chosen for obvious advantages. 1) The in ovo embryo is not affected by a matemal host and reacts directly to teratogenic agents; 2) A large sample population can be used to provide statistically meaningful results; 3) The chick embryo has been carefully described throughout all stages of development, allowing for the identification of any changes subsequent to NMR exposure; 4) Quail cells can be used as natural markers to study neural crest migration. Finally, the chick sympathetic system was chosen for studies of neural development because: 1) It is less complex compared to the central nervous system; 2) Extensive devclopmental studies have already been done in our laboratory; 3) The sympathetic system of the chick is similar to that of the mammal. The specific aims of this research will be pursued with very sensitive techniques and the results will be analyzed blindly to avoid bias. Morphological abnormalities will be microscopically examined and analyzed according to established developmental criteria. Behavioral tests will be recorded on videotape and carefully analyzed. Studies on the developing nervous system wifl utilize techniques that are routine in our laboratory. Thus, the migratory pattem of neural crest celis will be determined by a quail-chick transplantation technique. Axonal projections will be labeled by horseradish peroxidase (HRP) axonal tracing techniques and the pattern of specific ganglion cell innervation will be determined by intracellular recording techniques. Results of this systematic study should provide an important data base for the assessment of risks on NMR exposure during embryonic development.